Conventional technology provides for the drilling of a wellbore from the surface to a predetermined depth beneath the surface into a subterranean formation containing hydrocarbon reserves. Most conventional wellbores have traditionally been substantially vertical or perpendicular to the surface. However, current technology now provides for the drilling of deviated or non-vertical wellbores using directional drilling technology.
Directional drilling technology also allows for secondary, branch or lateral wellbores to be drilled laterally from a primary or main wellbore. A primary wellbore including more than one secondary or lateral wellbore is typically referred to as a multilateral well. Lateral wellbores are often drilled and produced through a gap in the casing of the primary wellbore. This gap typically comprises a window cut or milled in a section of the existing casing string. The lateral wellbore tends to extend laterally from the primary wellbore to a desired location within the formation.
As a result of the development of lateral wellbores, industry attention has more recently focused upon the difficulties associated with the completion of such wellbores. For instance, completion at the junction between the primary wellbore and the lateral wellbore is important in order to minimize any potential for the collapse of the well, as may occur in unconsolidated or weakly consolidated formations. The apparatus used for the completion of the junction between the primary and lateral wellbores preferably provides a means for hanging a conventional liner within the lateral wellbore, while hydraulically sealing the junction. As well, the apparatus used for completion preferably permits the diameter of the lined lateral wellbore to be as close as possible to the inner or drift diameter of the casing string of the primary wellbore in order to facilitate completion and servicing of the lateral wellbore and maximize production from the lateral wellbore.
U.S. Pat. No. 5,388,648 issued Feb. 14, 1995 relates to a number of methods and devices for completing lateral wells. Several of these methods and devices specifically relate to the completion and sealing of the junction between a vertical and lateral well. In particular, each of these methods and devices utilizes a "deformable means" to selectively seal the junction.
In one embodiment, the deformable means is comprised of an inflatable mold which includes an inner and outer bladder defining an expandable space therebetween for receiving a pressurized fluid. The mold must be comprised of a flexible plastic or rubber such that it is fully collapsible. The deformed or fully collapsed mold is run into the primary wellbore adjacent to the junction with the lateral wellbore. Pressure is then applied to cause the mold to take on a nodal shape having a laterally depending branch extending into the lateral wellbore. A slurry of hardenable or settable liquid (e.g. epoxy or cementitious slurry) is then pumped into the space between the mold and the wellbores to form a seal. In this manner, the hardenable liquid comprises a portion of the casing string of the wellbore. Thus, the mold is utilized during the setting and cementing of the casing string in the primary wellbore, and may not be particularly useful when the casing string is already formed in the primary wellbore.
In a further embodiment, the deformable means is comprised of an expandable memory metal device. The device includes a primary conduit section and a laterally extending branch. The lateral branch is made of a very specific material, being a shape memory alloy, which is fully deformed or collapsed during the insertion of the device into the primary wellbore. Once the device is positioned in the primary wellbore adjacent the junction with the lateral wellbore, heat is applied which causes the device to regain its original shape. As a result, the laterally extending branch extends into the lateral wellbore.
In a further embodiment, the deformable means is comprised of a swaging device for plastically deforming a sealing material. In particular, a liner is run through the primary wellbore and into the lateral wellbore. The liner includes a ranged element surrounding its periphery, which contacts the peripheral edges of the window in the casing string. A swage is then pulled through the primary wellbore, contacting the ranged element and forming a flange against the window of the casing. Thus, the ranged element is plastically deformed to form a seal at the junction.
In a final embodiment, the deformable means is comprised of a collapsible/expandable secondary string casing device, which device is run into the wellbore with the casing and forms part of the casing string. A window is milled into a length of a rigid primary casing body of the device. A collapsible/expandable secondary string casing, comprised of a special flexible alloy or a flexible plastic or rubber, is joined to the window in the primary casing body. The secondary string casing is collapsed to fit closely around the rigid primary casing body. and is run into position in the primary wellbore adjacent the junction with the lateral wellbore. Pressure is then applied to fully inflate the secondary string casing.
Each of these deformable means has inherent disadvantages in its use. For instance, a special flexible alloy, shape memory alloy or flexible plastic or rubber must be used to form all or a portion of the junction sealing device. Further, a portion of the device, typically the lateral branch or secondary string of the device, must be partially or fully deformable or collapsible in order to insert and place the device within the primary wellbore. As well, special swaging or pressure providing tools are often required to seal, inflate or expand the device within the primary wellbore. Typically, placement of the device requires plastic deformation of all or a portion of the device. Finally, the placement of the device may affect the setting and cementing of the casing string in the primary wellbore.
As a result, there remains a need in the industry for an improved apparatus and method for the completion of a wellbore, and in particular, for the completion of the junction between the primary and secondary or lateral wellbores. Preferably, the apparatus and method provide a means or manner of hanging a conventional liner within the secondary wellbore, while hydraulically sealing the junction between the primary and secondary wellbores. As well, the apparatus and method preferably allow a full bore drill out, in that the diameter of the completed secondary wellbore is about equal to the inner or drift diameter of the casing string in the primary wellbore.